Lists of Nobel Prizes and Laureates

Lists of Nobel Prizes and Laureates

Otto Meyerhof and the Physiology Institute: the Birth of
Modern Biochemistry

Ludolf von Krehl's search for colleagues
who would integrate the then quite separate disciplines of the
natural sciences under the umbrella of biomedical research led
him to Otto
Meyerhof. Meyerhof's study of intermediate metabolism
involved a mix of physiology, pharmacology, physics and
pathology. His already well-known successes with the study of
muscle physiological chemistry, for which he had won a Nobel
Prize in 1922, made him a logical choice as head of the KWImF's
proposed Physiology Institute.

Otto
MeyerhofPhoto: Courtesy of Walter Meyerhof, son of
Otto Meyerhof

The years Meyerhof spent at the KWImF
represent the most important and productive phase of his
brilliant career. Indeed, some scientific historians,
including Thomas Kuhn, believe the work during the 1930s in the
laboratories of Meyerhof, Parnas, Embden, Warburg and a few
others was the mark of true scientific revolution. While in
Heidelberg, Meyerhof and his assistants published over 200
articles and played a central role in piecing together the
complex puzzle of glycolysis - a major milestone in the study of
intermediary metabolism. Meyerhof and his colleagues not only
discovered a major proportion of the chemical compounds involved
in this metabolic pathway, but played a key role in determining
how and in which distinct sequence those compounds chemically
interact. In the process, they pioneered our understanding of how
energy is biochemically transformed, stored and released for work
in the cell.

Meyerhof attracted a steady stream of
remarkable assistants and students to the KWImF in Heidelberg.
The chemist Kurt Lohmann was clearly Meyerhof's right hand man
during this time. It was he who first discovered ATP - the
molecule now known as the universal energy donor. Lohmann and
Meyerhof also made the critical structural and functional studies
of this all-important molecule while at the KWImF. The Physiology
Institute was, however, far more than a two-man show. Hermann
Blascko, David Nachmansohn, W. Kiessling, Paul Ohlmeyer, Severo Ochoa, Fritz Lipmann, George Wald and
André
Lwoff all worked in Meyerhof's laboratory during the 1930s.
The latter four went on to win Nobel Prizes of their own after
leaving the KWImF. These men and other students of Meyerhof
enthusiastically took forward the torch of the Meyerhof School to
other institutes and nations in the years that followed.

Prelude to the Study of Intermediate Metabolism

The forerunners to Meyerhof's work on
intermediate metabolism can be traced back to the late 18th
century, when Lavoisier introduced the concept
of respiration as the combustion of carbon and hydrogen in the
lungs. By the mid-19th century, scientists, especially in France
and Germany, had formulated critical questions about how organisms
gradually break down and use foodstuffs. Yeast and muscle were
the focus of most of these early studies. Glycogen, the sugar
that figures so prominently in the metabolic pathway linked with
Meyerhof's name, had been discovered in the 1850s and oxidation
and fermentation were proposed as the mechanisms by which such
sugars are utilized. Lactic acid, the focus of many of Meyerhof's
early studies - was known to accumulate in muscle tissue and was
considered a by-product of fermentation in muscle, much as alcohol
and carbon dioxide are by-products of yeast fermentation.

Progress slowed during the second of half
of the 19th century, although critical advances in inorganic and
organic chemistry helped to usher in a new era for physiological
chemistry. Just before the turn of the century, scientists began
to forcefully formulate the chemical reactions that occur within
cells. In 1897, Eduard Buchner provided
a major turning point with celebrated studies on alcoholic fermentation.
Buchner had isolated the enzyme responsible for fermentation from
yeast-press juice. This enabled him to do controlled experiments
with cell-free chemical fermentation. This was the first demonstration
of biological processes outside of the living cell. Buchner's
work was important for several reasons: first, it discounted long
held and popular vitalistic theories that considered cellular
processes as fundamentally different from other principles of
chemistry; second, it introduced a methodology that would allow
scientists to break down biochemical processes into their individual
steps; and, finally, the discovery of cell-free fermentation had
opened the doors to one of the most important concepts in biochemistry
- the enzymatic theory of metabolism.

In 1906, Harden and Young elaborated
upon Buchner's work by showing that complementary enzymes - coenzymes
- are also crucial to such processes. During the next decade,
scientists like Carl Neuberg, Gustav Embden and Jacob Parnas made
major contributions to early metabolic studies in yeast. The answers
to how such processes work would take another three decades, but
methodology and the way scientists formulated their questions
about metabolism had entered an entirely new phase.

The Beginning of Meyerhof's Career in Science

Ludolf von Krehl was building up a small research
program on metabolism at his University of Heidelberg Medical
Clinic at the same time that Otto Meyerhof was finishing up his
medical studies in Heidelberg. Otto Warburg, who had
been a student of Emil
Fischer, had joined Krehl in 1906. When Krehl offered Meyerhof
his first research position in 1909, it was Warburg's responsibility
to teach the newly graduated physician his techniques for investigations
of respiration, oxygen consumption and growth rates in sea urchin
eggs. Warburg's innovative ideas and dynamic, self-confident approach
had a dramatic impact on Meyerhof, inspiring him to focus his
career on physiological chemistry. Meyerhof worked at Krehl's
laboratory for little over two years, but the establishment of
ties with Krehl and development of a close friendship with Warburg
were to be factors which would continue to shape Meyerhof's career.

After leaving Heidelberg, Meyerhof took a
position at the University of Kiel, where he quickly began to
make a name for himself. In 1913, he presented an epoch making
lecture on the energetics of living cells. This was one of the
very first adaptations of the physical laws of thermodynamics
to physiological chemistry. Meyerhof's goal was to understand
how energy is transformed during chemical interactions in the
cell. He recognized that between initial energy input via food
and its final dissipation as heat, a series of intermediate steps
to transform that energy must occur to maintain the organism in
a state of dynamic equilibrium. With minor revisions, his theory
on the thermodynamics of living matter remained influential for
decades.

In his ensuing efforts to relate energy transformations
and chemical changes to cellular function, Meyerhof turned his
attention increasingly toward experimentation with muscle, where
such transformations promised to be large enough in scale to test
his new theory.

Meyerhof was also interested in analogies
between oxygen respiration in muscle and alcoholic fermentation
in yeast and the role that enzymes played in both. 1918 marked
the first experimental milestone in Meyerhof's career, when he
showed that a coenzyme involved in the production of lactic acid
in muscle was the same coenzyme as Harden and Young had found
involved in alcohol fermentation in yeast. This was important
early evidence of the unity in life of fundamental biological
processes.

In his 1913 address, Meyerhof had mentioned
the work of the Englishman, A.V.
Hill. Hill had pioneered methods to measure heat production
in biological processes. Since Meyerhof's lecture, Hill had found
a pattern of discrete temperature changes during muscle contraction
and relaxation that suggested a complicated series of biochemical
interactions. This reminded him of work by Fletcher and Hopkins
in 1907, which had shown that lactic acid increases in resting
muscle in an oxygen-free environment, but then disappears when
oxygen is reintroduced. Hill noted that his own measurements of
heat during anaerobic conditions correlated strikingly to Fletcher's
and Hopkins' results. This was important evidence for the theory
that lactic acid was not simply a by-product of muscle activity,
but must be a part of the muscle machinery itself.

Soon after the end of WWI, Meyerhof began
collaborating with A.V. Hill. Both men were convinced that a key
to understanding metabolism lies in quantitatively correlating
data on heat development, mechanical work and cellular chemical
reactions. In Germany, Meyerhof focused on chemical methods to
measure oxygen consumption, the conversion of carbohydrates, lactic
acid formation and decomposition, then correlating it to thermodynamic
data and various phases of muscle activity.

Between 1918 and 1922, Meyerhof worked out
an extraordinary amount of this biochemical detail, including
proofs that it is glycogen that is converted into lactic acid
in the absence of oxygen. He also showed that in the presence
of oxygen, only one-fifth to one-fourth of lactic acid production
during anaerobic contraction of the muscle is subsequently oxidized
to carbon dioxide and water. Thus, Meyerhof tied the release of
energy during this particular oxidation to the reconversion of
the remaining four fifths of the lactic acid back to glycogen.

These results had several important ramifications:
they explained the course of heat production measured by Hill;
and they confirmed and extended a famous theory of Pasteur's that
less glycogen is consumed in muscle metabolism in the presence
of oxygen than in its absence. The depression of glycolysis by
respiration was thereafter referred to as the Pasteur-Meyerhof
effect. This would be significant later on in working out the
full details of the glycolytic pathway. Finally and most importantly,
the conversion of glycogen to lactic acid and back again to glycogen
was the first evidence of the cyclical character of energy transformations
in living cells. Meyerhof called it the lactic acid cycle. Meyerhof
and Hill's analysis of this cycle and its relation to respiration
earned both men the Nobel Prize in 1922.

A Nobel Prize Winner Struggles for Respect: Warburg and the
KWG Come to the Rescue

Meyerhof's early achievements were amazing
given the conditions under which they were performed. WWI interrupted
his experimentation and delayed contact with Hill. He worked virtually
alone during his years in Kiel; the one exception was a six-month
period after his Nobel Prize was announced, during which time
Hans Hermann Weber served as his assistant (this fact is notable
because Weber was later called upon to direct the MPImF Physiology
Institute in the 1950s). Anti-Semitism and resentment over Meyerhof's
pacifism during the First World War were largely responsible for
the conspicuous lack of support from the faculty at Kiel. Despite
his Nobel Prize and solid recommendations from outside referees
and his department chair, Meyerhof was denied promotion at the
University. Indeed, he encountered great difficulty finding a
suitable position anywhere in Germany during this period.

Meyerhof became depressed and was at the point
of emigration when his old friend Otto Warburg, who now directed
one of the Kaiser Wilhelm Institutes in Berlin-Dahlem, began lobbying
KWG President Adolf von Harnack on his behalf. In late 1924, Warburg
made Meyerhof a stop-gap offer of space in his own institute.

Although the facilities Warburg offered were
cramped, they were a major improvement over the instability of
Kiel. And with its collection of brilliant physicists, chemists
and biologists, the complex of KWIs in Berlin-Dahlem promised
an intellectually stimulating environment for Meyerhof. He accepted
and during the next five years was able to build a small research
team to help him unravel the lactic acid cycle. Thus, it was in
Berlin that Meyerhof began to truly lay the groundwork for the
brilliant successes that were to follow at the KWImF in Heidelberg
during the 1930s.

Two noteworthy scientific trends that were
taking place during this time should be mentioned. The first revolved
around the recognition of the importance of enzymes in the metabolic
pathways and corresponding methodological advances in enzyme chemistry.
Many research groups throughout the world made significant contributions
in this regard, but Berlin-Dahlem was a particular center for
this work, with the Big Three of Warburg, Neuberg and Meyerhof
working in close concert with one another. The second trend began
with the discovery of a compound called creatine phosphate. This
excited new interest in the possible role that phosphates might
play in energy transfers and set many other research groups in
a search of similar phosphorylated compounds that might be involved
in yeast fermentation and muscle glycolysis.

With the introduction of thermodynamics, advances
in enzyme chemistry and the discovery of phosphorylated compounds
in the 1920s, the stage was set for a sudden shift in how scientists
understood intermediate metabolism. That shift would take place
almost immediately after the arrival of Meyerhof at the new KWImF.

Meyerhof is Reunited with Krehl in Heidelberg

Otto Warburg had been Ludolf von Krehl's first
choice as director of the KWImF Physiology Institute. And although
Warburg decided to stay in Berlin, he remained a close advisor
to Krehl and the KWImF throughout the late 20s and 30s. Given
Meyerhof's subject area, his credentials and the inadequacy of
facilities in Berlin-Dahlem befitting his international stature,
it is not surprising that Warburg strongly encouraged Krehl to
offer the position to his friend and trusted colleague. It helped,
of course, that Krehl knew Meyerhof personally from his earlier
years in Heidelberg, but accepting a Nobel Prize winner as second
choice was hardly a bitter pill for Krehl to swallow. The avalanche
of results in Meyerhof's institute during the next 8 years would
certainly prove the worthiness of the choice.

For his part, Meyerhof never hesitated at
Krehl's enticing offer. Given the exciting intellectual environment
that existed at Berlin-Dahlem, Meyerhof's excitement was a testament
both of his respect for Krehl's vision and the magnificence of
the new facilities. The reunification with Krehl seemed to be
a dream come true. Finally, after so many years of struggling
against non-scientific barriers, Meyerhof believed he would be
able to concentrate his full attention upon his work.

Meyerhof's assistants were crucial to his
success in Heidelberg. Fortunately, he was able to bring with
him the critical members of his team from Berlin-Dahlem. This
minimized the transition time. As it turned out, those first months
were extremely important. The original group included Kurt Lohmann,
the expert chemist who worked with Meyerhof for nearly 13 years,
Fritz Lipmann, David Nachmansohn, Hermann Blaschko, and Severo
Ochoa, as well as his trusted technician, Walter Schulz. Meyerhof's
reputation for innovation and his holistic approach also served
as a magnet for other talented young scientists who made major
independent contributions at the KWImF. During the next eight
years, Ken Iwasaki, Paul Rothschild. M. Dubuisson, George Wald,
Alexander von Muralt, André Lwoff, W. Kiessling, H. Lehmann
and Paul Ohlmeyer took their turns at the Physiology Institute.
Frequent visits by guest scientists, such as Einar Lundsgaard,
A.V. Hill, Otto Warburg, and Hans Krebs also contributed
greatly to the intellectual mix.

Meyerhof's broad philosophical approach to
his work and personal generosity set the tone for an enthusiastic
collaborative environment that evolved at his institute. His research
group had a tremendously international flavor. Discussions were
frequent, open and unusually informal for the time. This included,
especially for younger scientists at the laboratory, frequent
contacts with colleagues in Richard Kuhn's chemistry
institute. Years later, many of the scientists who had worked
with Meyerhof during these years fondly recalled their time at
the KWImF, both as a tremendously exciting scientific experience,
but also as a time in which life-long friendships and professional
networks were initiated.

Meyerhof (left) seated beside A.V. Hill, with whom he won
the Nobel Prize, at the KWImF around 1931. Standing in the
background from left to right are Karl Lohmann, Alexander
von Muralt, Grigore Alexandru Benetato, Hermann Blaschko,
Arthur Grollman, H. Laser, his technicians Fischer and Schulz
and Eric Boyland.Photo: Courtesy of Max-Planck-Institut für
Medizinische Forschung

Research Breakthroughs at the KWImF Physiology Institute

By late 1929, it was clear that solving muscle
glycolysis would be far more challenging than anyone had imagined.
The sheer number of components and the short-lived nature of many
of the chemical interactions made the task of sorting out the
pathway imposing. Understanding glycolysis was like putting together
a giant puzzle. To complicate matters, many of the pieces were
still missing from the table. Some that had been found had to
be laid to the side until the pieces that fit around them were
discovered or put in place. Moreover, it was just becoming clear
to Meyerhof that some of the chemical components had been forced
into the wrong portion of the puzzle, confusing the overall picture.

A tremendous amount of patience and man-power
over a thirty year period had already been focused on this one
scientific problem simply to allow a vague outline of glycolysis
to emerge. As in any puzzle, however, the discovery of a few key
components can lead to a rapid series of related discoveries.
This was certainly the case in November of 1929, after which the
pieces of Meyerhof's puzzle began to fit into place at an accelerating
pace.

When Meyerhof arrived at the KWImF, he still
emphasized thermodynamics and enzyme chemistry in studies of striated
frog muscle, but his analysis and methodology were evolving and
growing in scale. As data mounted, he and his assistants began
to explore the sequence of minute chemical interactions of glycolysis
at a much deeper level. Moreover, while his early model - the
lactic acid cycle -had led to significant new discoveries, these
new discoveries were now forcing Meyerhof to reformulate
his famous theory. Meyerhof and his students' experimental approach
at Heidelberg contributed greatly to this success. They were unusually
accomplished at breaking down glycolysis into its many separate
components, analyzing each step separately, then reassembling
the constituent parts within an overall system. Their thermodynamic
studies of a wide range of phosphorylated compounds were particularly
important at the beginning of the Heidelberg years, while identification
and analysis of intermediate products such as esters and the enzymes
that catalyze the biochemical reactions became increasingly important
during the latter years. Meyerhof also included many comparative
studies of intermediate metabolism in other muscle types, animal
tissues, as well as fermentation in yeast and bacteria.

Meyerhof and his colleagues at the KWImF remained
squarely at the center of this field of research during this dynamic
period of discovery. It should be emphasized, however, that other
scientists also made important contributions. Parnas, Neuberg,
Warburg, Needham, Wieland, the Coris, Embden, Fiske,
and others made discoveries that cannot be detailed here. In fact,
Meyerhof's continuing success during the 1930s was partially due
to his lack of arrogance about his own ideas. As we will see,
he critically and enthusiastically examined the work of others
in the field and was quite capable of altering his own theoretical
concepts when new evidence indicated its appropriateness.

Lundsgaard and the Demise of the "Meyerhof Cycle"

Meyerhof and Hill's pioneering thermodynamic
studies had been the basis for the conclusion that the cycle of
lactic acid formation and oxidation were the key events in glycolysis.
From 1922 until almost 1934, most scientists believed that energy
production and mechanical work in muscle were directly coupled
to the production of lactic acid. Indeed, after a much heated
debate with Embden, who believed that a molecule called lactocidogen
was the energy source for the muscle mechanism, this idea became
known in some circles as the Meyerhof dogma. Ironically, the discovery
in 1926 of the compound creatine phosphate had already caused
Meyerhof to publicly question the certainty of his own theory
before most other scientists did. Still, in the absence of a better
model (e.g. Embden's lactocidogen proved not to be the activator),
Meyerhof continued to support the general theory of the lactic
acid cycle, and much of his group's efforts during the late 20s
continued to be directed toward unravelling lactic acid's role
in muscle glycolysis.

The real turning point in Meyerhof's adherence
to the lactic acid cycle came with the arrival of a letter at
the new KWImF from the Danish physiologist, Einar Lundsgaard.
Lundsgaard told Meyerhof that he had found muscles poisoned with
iodatica acid contracted without the production of lactic acid
- if creatine phosphate were added to the solution. The ability
to contract without lactic acid seemed to contradict Meyerhof's
famous theory. This surprised and excited Lundsgaard. He included
in his letter a preprint of his paper suggesting creatine phosphate's
possible direct involvement in muscle contraction. Lundsgaard
also asked if he could come to the new KWImF to test his findings
using Meyerhof's thermodynamic methods. Although Lundsgaard's
data seemed to undermine Meyerhof's famous theories, he agreed
immediately to the Danish scientist's request.

Due of the close relation between the lactic
acid cycle and the transfer of energy in muscle, Meyerhof still
believed that this set of biochemical changes was critical
to understanding the mechanism of contraction. He was, nevertheless,
impressed with Lundsgaard's initial results. Moreover, recent
experiments in his own laboratory by David Nachmansohn also suggested
a correlation between creatine phosphate and the speed of muscle
contraction. If Lundsgaard's and Nachmansohn's results were accurate
and related, Meyerhof realized he would have to reformulate his
model.

When Lundsgaard arrived at the Heidelberg,
Lipmann met him at the railway station and brought him straight
to the laboratory. Meyerhof and the two younger scientists began
experimenting even before Lundsgaard could unpack. Lundsgaard
stayed at the KWImF for over six months in 1930, during which
time Meyerhof, Lohmann, Lipmann and Blaschko worked with him to
refine and extend his initial work.

The early data at the KWImF initially pointed
to the phosphorylation of creatine phosphate as the primary event
in muscle contraction and, during the next 18 months, much attention
was focused on in vivo and in vitro studies of this
compound. Lipmann and Nachmansohn, in particular, concentrated
on measuring the breakdown and synthesis of creatine phosphate
during muscle activity, carefully correlating rates to energy
release, muscle tension and simultaneous lactic acid production.
In 1931, Meyerhof formally bid farewell to his once favored view
that lactic acid itself plays a role in the mechanism of contraction.
The new data left him with no doubt that hydrolysis of creatine
was of the utmost importance to the contraction mechanism. Meyerhof
now tentatively proposed that lactic acid formation supplied the
energy for the continuous resynthesis of creatine phosphate at
the moment of contraction.

Meanwhile, the discovery of other phosphorylated
compounds, esters and enzymes also contributed to the demand for
a theoretical overhaul of glycolysis and related mechanisms of
contraction. Although much more needed to be investigated, Meyerhof
confidently expressed the hope that in a few more years a working
hypothesis would emerge to bring order into the mass of new facts
that his group and others were rapidly accumulating.

The Discovery of ATP and its Importance as Universal Energy
Donor

Of course, it was ATP, not creatine phosphate,
which proved to be the critical source for free energy in glycolysis.
But the road to its discovery and understanding of its critical
and almost universal role as energy provider in cellular processes
began with and led through the analysis of creatine phosphate.

Creatine phosphate was discovered simultaneously
in 1926 by Fiske and SubbaRow at Harvard University and the Eggletons
in Hills laboratory in England. Until this time, scientists had
largely ignored phosphates as important in metabolism. In addition
to spawning Meyerhof's first doubts about the centrality of lactic
acid in glycolysis, the discovery encouraged him to begin measurements
of the amount of energy released by the splitting of the bonds
of creatine phosphate and other phosphate derivatives. When Gustav
Embden isolated adenosine monophosphate (AMP) in 1928, Meyerhof
and others began a serious search for other phosphates involved
in glycolysis and yeast fermentation.

In late 1928, Kurt Lohmann isolated salts
of a new phosphorylated compound from muscle, which he called
PP. Karl Meyer, who also worked for Meyerhof, had just found the
co-factor related to lactic acid formation while attempting to
extract enzymes from frog muscle. Identification of this co-factor
was turned over to Lohmann at the direction of Meyerhof. In December,
Lohmann identified the co-factor as a combination of Embden's
AMP and PP. The compound was adenosine triphosphate, commonly
referred to today as ATP.

Adenosine Triphosphate (ATP)

All living cells must create order
within themselves to survive and grow. This is thermodynamically
possible only because of a continuous input of free energy,
part of which is released from cells to their environment
as heat.

The ultimate source of energy for living cells is sunlight, captured
by plants and stored in the carbon bonds of carbohydrates. Animals
get energy by eating carbohydrates and oxidizing them in a series
of enzyme catalyzed reactions that are coupled to the formation
of adenosine triphosphate (ATP). When the high energy of phosphate
bonds of ATP are broken during cellular metabolism, free energy is
made available for a wide range of biological activities, including
muscle contraction, nerve excitation, membrane transport, as well
as the manufacture of proteins and nucleic acids.

Adenosine triphosphate, or ATP, was
first discovered in muscles by Otto Meyerhof's assistant
Kurt Lohmann just a few months before the opening of the
KWImF in Heidelberg. At the time of its discovery, ATP's
role in the biological processes of organisms, from bacteria
to mammals, was not recognized. Its central importance
came sharply into focus during the next few years, as
Meyerhof and his colleagues in Heidelberg worked out step
after step of the glycolytic pathway. Lohmann, who worked
with Meyerhof from 1924-37, played the dominant role in
discovering and unraveling the structure and function
of this famous molecule.

Whether it was intuition, inside information
or general practice regarding timely publication, Meyerhof pushed
Lohmann to submit his data. It appeared in early August of 1929
in the journal Naturwissenschaften. Although Fiske and SubbaRow
had almost certainly simultaneously purified salts of ATP at
Harvard University, through an ill-fated decision, they chose
not to publish their own results. In late August, Lohmann presented
the discovery of ATP at the International Physiology Conference
in Boston. Fiske, who attended the lecture, must have sensed
his mistake, because he immediately approached Lohmann after
the talk and a low-key argument broke out, as witnessed by Severo
Ochoa. Fiske and SubbaRow quickly arranged to give an informal
talk at the end of the conference and rushed to publish their
own data in October. It was too late, however. Priority for
the discovery of ATP was awarded to Lohmann.

None of the talks or paper, either by Lohmann
or Fiske and SubbaRow, even suggested the huge ramification
that this discovery might have for biological processes. In
fact, outside of Fiske's reaction, Lohmann's presentation at
the Physiology Conference evoked little response from those
in attendance.

Lohmann's presentation in Boston of the
discovery of ATP came only two months before Meyerhof and his
group were to move to the new KWImF. For this reason, there
had been no time for the thermodynamic measurements of heat
release or structural or functional studies at Berlin-Dahlem.
The real meaning of the discovery of ATP would have to wait
until follow up work occurred in Heidelberg. This analysis would
prove to be a much more daunting and important task than ATP's
initial discovery.

Although Lundsgaard's work helped Meyerhof's
group recognize the importance of phosphate derivatives, their
initial excitement over creatine phosphate pushed analysis of
ATP on the back burner for more than a year. Its role surfaced
only gradually as Meyerhof's group patiently broke the glycolytic
pathway into its individual steps and analyzed them.

The first hint of ATP's real importance
took place within the thermodynamic studies that Meyerhof had
ordered for the various phosphorylated compounds. Lohmann and
Meyerhof had begun to group phosphate derivatives into two essential
categories - one group characterized by low energy release and
one by high energy release upon splitting of their bond. In
1931, Lohmann found that ATP generated considerable heat when
split to AMP and two inorganic phosphates. The results placed
ATP in the same class of high energy phosphates as creatine
phosphate. With these results in hand, Meyerhof encouraged closer
examination of ATP, its correlation with other data and interactions
with other molecules.

In 1932, Lohmann published an initial chemical structure of ATP.
Although he would modify the structure slightly over the next three
years, this first paper disproved several prominent competing models
and contributed greatly to the momentum of related discoveries at
the KWImF. In 1935, Lohmann proposed his refined structural model
of ATP, which was confirmed in the late 1940s after the introduction
of new X-ray crystallographic techniques.

1932 was also the time Meyerhof's group
first made associations between the uptake of phosphate during
the breakdown of carbohydrates to lactic acid and the splitting
of ATP. They found that ATP is resynthesized in subsequent reactions.
This was the first suggestion that the lactic acid cycle participates
in the maintenance of the formation of ATP. By 1934, Lohmann
provided direct evidence that ATP synthesis was the by-product
of utilization of glucose.

Meyerhof and Lohmann continued to refine
their data and analysis. One milestone came in 1934 when Lohmann
observed that phosphate molecules from creatine phosphate combine
with adenylic acid to form ATP, yet without producing heat.
This was the first recognition that high energy compounds could
accomplish a biochemical reaction without heat production. These
experiments, as well as similar ones by Parnas, pointed to the
role of creatine phosphate as a storehouse of energy for phosphorylating
ATP. It confirmed and explained the association of creatine
phosphate with the speed of muscle contraction that had been
suggested by David Nachmansohn's earlier experiments. Work by
Lohmann and Meyerhof, along with important contributions by
Parnas, also established the necessity of AMP or ADP in such
reactions.

Parnas soon postulated a phosphate cycle,
whereby the use of one ATP for phosphorylation is balanced by
regeneration of ATP during subsequent steps in glycolysis. If
this sounds similar to Meyerhof's old lactic acid cycle, it
is no coincidence. As the structural and thermodynamic data
about ATP mounted, combined with the enzymatic information and
the discovery of myosin, Meyerhof was finally in a position
to formally propose that the release of energy in ATP hydrolysis
was the primary event leading to muscle contraction and that
lactic acid and creatine phosphate were only indirectly involved
through their role of maintaining the ATP cycle.

Of course, we now know that ATP is widely
utilized in reactions involving energy transfer in all cells,
as well as in bacteria. The discovery of ATP was, thus, the
key that opened up the floodgates to understanding many conversion
mechanisms of metabolic energy. The unravelling of its structure
and bioenergetic role in glycolysis clearly stands out as a
major scientific accomplishment.

The Role of Other Intermediate Compounds

Although ATP plays a critical role in glycolysis,
it is only one actor among many in a very large production.
Meyerhof's greatest achievement was his ability to clarify both
the starring and supporting roles of the many molecules involved
in glycolysis and then place them in proper sequence of the
metabolic script. As research director, this is where Meyerhof's
theoretical insight, holism, openness to new ideas and, indeed,
creativity came critically into play.

During the years before Meyerhof came to
Heidelberg, a good number of chemical compounds involved in
muscle contraction had been found, including lactic acid, pyruvate,
methylglyoxyl, hexosediphosphate, AMP, creatine phosphate, as
well as several enzymes. That number dramatically increased
during the 1930s. The challenge now facing Meyerhof was to identify
the specific roles played by each compounds in the complex chain
of chemical interactions that lead to the release of energy
that drives muscle contraction.

Meyerhof ordered a broad series of tests,
especially on esters and enzymes. There were many questions
to be answered. For example, what was the chemical nature of
each compound? From which other compounds along the pathway
did they derive? With which components did each interact in
the next step along the pathway? What new compounds were formed
or waste products left behind? How did pH and temperature affect
the reactions? What enzymes initiated each reaction?

Answering such questions was a challenge
because most of the components involved in glycolysis were typified
by a very transient existence, making them difficult to isolate,
much less analyze, test and then place in proper sequence. Meyerhof
ordered experiments with intact muscle, but one must understand
that many productive in vivo techniques that we now take
for granted, such as using isotopes to tag and trace molecules
along the pathway, did not yet exist. Thus, in vitro studies,
in which each step along the pathway could be broken down and
studied separately, became Meyerhof's main tool for studying
glycolysis. These methods required patience and determination.
They sometimes led to experimental artefacts, but their careful
application was ultimately the key to Meyerhof's great success.

One of most important advances of the decade
involved painstaking work that helped demonstrate that the formation
of esters from carbohydrates is indeed an intermediate reaction
in glycolysis. Influential scientists like Neuberg and Harden
had found the accumulation of esters like hexosediphosphate
during their earlier studies of yeast fermentation, but they
had relegated the accumulation of such compounds to the status
of a side reaction in the pathway. A few scientists, like Meyerhof,
Embden, and von Euler, differed
in this view point. Embden believed that the appearance of hexosediphosphate
was related to his lactocidogen, while Meyerhof proposed early
on that all glucose must go through esterification leading to
formation of phosphates. At the time, very little was known
about esters and such ideas were quite controversial and not
yet backed up by firm data. In fact, the critical role of phosphates
in biological interactions remained to be proven to many scientists
in the field.

Meyerhof was convinced that an active form
of hexosemonophosphate was an intermediate in glycolysis and
associated with the formation of pyruvate. But the sequence
of steps between formation of these molecules was unknown. Reactions
leading to esterification were particularly difficult to identify,
because these processes take place at different levels of glycolysis.
This picture only gradually became clear as Meyerhof and others
simultaneously worked out the cyclical process of glycolysis
and the reversibility of certain reactions. It also required
the discovery of different enzymes involved in esterification
of glucose and polysaccharides and then their purification in
order to experiment with the different steps in their in
vitro studies. Similar studies on many other compounds and
chemical reactions were made throughout the thirties in an effort
to fit them into the steps along the pathway.

The Unraveling of the System of Enzymes

During the 1920s, Neuberg, Warburg and Meyerhof
had already broken entirely new ground with direct applications
of enzyme chemistry to metabolic studies. Neuberg's famous work
with yeast was probably the birth of the idea that every biochemical
reaction is controlled by a specific enzyme. Warburg had
became the dominant authority on enzymes in respiration. Meyerhof
had managed to isolate and purify the co-enzyme (it turned out
to be a complex of enzymes) responsible for conversion of glycogen
to lactic acid in muscle. He had then reconstructed the main
steps of this complicated set of reactions in cell free solution.
He also had applied the same co-enzyme successfully to yeast
fermentation, providing earlier proof for the highly similar
molecular nature of these two biological processes.

After Meyerhof arrived in Heidelberg, the
identification of the individual reaction steps of the metabolic
pathways in yeast and muscle glycolysis were increasingly coupled
with the study of enzyme mechanisms. Once again, Meyerhof's
group was among the avant-garde of scientists involved in this
search. During the next eight years, they discovered more than
a third of the enzymes of glycolysis, with eight other research
groups combining to find the rest. Lohmann, Kiessling, Schuster,
Lehmann and Ochoa were most active at the Physiology Institute
in identifying, characterizing and partially purifying these
enzymes. Meyerhof's close relationship to Warburg was of great
help here, for it was he who developed new rapid and efficient
techniques to purify and crystallize enzymes

Table
adapted from that of Marcel Florkin in Chapter
24, Vol 31 of Comprehensive Biochemistry.

Early on, Meyerhof's group spent considerable
effort to investigate the effects of hexokinase, which Meyerhof
had discovered in 1927. This enzyme rapidly increased the formation
of lactic acid and esterification of hexosediphosphate in muscle
extracts. Hexosekinase was later found to catalyze the first
step of glycolysis by transferring a phosphate group from ATP
to glucose to form glucose-6-phosphate. This put an end to the
idea of direct phosphorylation of glucose by inorganic phosphate.

In 1932, Lohmann was also the first to detect
creatine kinase activity in muscle. This enzymatic reaction
is involved in the splitting of creatine phosphate during muscle
contraction (the structure of creatine kinase was just recently
solved at the MPImF by W. Kabsch in Professor Ken Holmes' Department
of Biophysics). By 1934, Lohmann had experimentally confirmed
this important reaction, providing for the first time the description
of the mechanism for utilization of phosphate energy. It subsequently
became known as the Lohmann Reaction. In 1933, he identified
the enzyme responsible for establishment of an equilibrium between
glucose-6-phosphate and fructose-6-phosphate. He also
found thiamine pyrophosphate to be a co-enzyme, which Severo
Ochoa later showed was required for oxidation of pyruvic acid.

Embden-Meyerhof Cycle

In the case of glycolysis and alcohol fermentation
in yeast, theoretical models and research clearly formed a positive
feed-back loop. As in all science, theoretical models are not
only an attempt to explain data, but are used to inspire
new experimental approaches. Until the mid-thirties, the attempts
to test models for alcohol fermentation and glycolysis had more
often than not disproved the theoretical constructs. This included,
of course, Lundsgaard's dismantling of Meyerhof's own lactic
acid cycle. Likewise, in 1932, discoveries in the laboratories
of Meyerhof and von Euler in Sweden finally undercut the
methylglyoxal theory, which had long been favored by many as
a way of understanding the pathways in yeast. During the early
1930s, each new discovery of an enzyme or intermediate component
led to more data. Working out the importance of the phosphorylated
compounds in muscle, for example, greatly stimulated the understanding
of energy transformations in glycolysis and changed thinking
about how the pathway might be constructed. The understanding
of the individual reactions in glycolysis grew geometrically.

By 1932, a cohesive and accurate model of
the entire pathway was still clearly needed. Indeed an accurate
model for the cycle was just around the corner. It came from
one of Meyerhof's major competitors, Gustav Embden. With accumulating
data from his own and other laboratories, Embden constructed
a detailed proposal for reaction sequences for almost the entire
pathway. The model would prove amazingly accurate. Unfortunately,
Embden died in 1933 before he had an opportunity to play a major
role in testing the theory.

Meyerhof quickly recognized the great value
of Embden's model. During the next five years, the research
groups of Meyerhof, Parnas, Needham, Warburg, Cori, and von
Euler effectively worked out the details of glycolysis. Without
question, the lion's share of these reaction steps were analyzed
at the KWImF. For this reason, glycolysis has been referred
to ever since as the Embden-Meyerhof

Recognition
of the Intermediary Steps of the Glycolytic Pathway

Date

Step

Authors

1911

Pyruvic Acid

Neuberg and
Wastenson

1928

Acetaldehyde

Neuberg and
Reinfurth

1933

D-3-Phosphoglyceric
acid

Embden, Deuticke
and Kraft

1933

F-1,6-PP

Embden, Deuticke
and Kraft

1934

G-6-P, F-6-P

Meyerhof

1934

2-Phosphoenolypyruvic
acid

Lohmann and
Meyerhof

1934

Phosphodihydroxyacetone

Meyerhof
and Lohmann

1935

D-2-Phosphoglyceric
acid

Meyerhof
and Kiessling

1936

D-Glyceraldehyde-3-P

Meyerhof,
Lohmann and Schuster

1936

G-1-P

Cori and
Cori

1939

D-1,3-Diphosphoglyceric
acid

Negelein
and Brömel

Table
adapted from that of Marcel Florkin in Chapter 24,
Vol 31 of Comprehensive Biochemistry.

Meyerhof had long been convinced of the
similarity of basic molecular processes in all life forms. He
had argued as early as the twenties in favour of the unified
pathway in yeast fermentation and glycolysis. Although he is
most famous for his work involving muscle contraction, he injected
considerable energy during the Heidelberg years into comparative
studies with yeast. As they delved deeper into the pathways,
he and his colleagues found the reactions and intermediates
in muscle and yeast cells to be extremely similar. Indeed, much
of the critical identification of glycolytic enzymes in Meyerhof's
laboratory was done in connection with experiments on yeast.
In 1935, with great assistance from Kiessling, Meyerhof was
able to experimentally confirm that with only minor differences,
the metabolic pathways in muscle and yeast were indeed the same.

Recognition of the unified pathway of glycolysis
represented major progress and was a turning point in silencing
those who argued that unity at the molecular level could not
exist. In search of further support for the concept of molecular
unity, Meyerhof searched for the occurrence of similar reaction
patterns in other biological materials throughout his tenure
in Heidelberg, including important studies on different types
of muscle, as well as bacteria. This led to the discovery of
phosphoarginine in the muscle of invertebrates, which serves
a similar role to that of creatine phosphate in vertebrates.

The Threat of National Socialism Finally Forces Meyerhof to
Flee Heidelberg

Not surprisingly, the rise of the National
Socialism in Germany had a dramatic impact upon the development
of the KWImF Physiology Institute. Meyerhof watched painfully
as close colleagues and students, like Blaschko, Lippmann, Neuberg,
Nachmansohn, Ochoa, Krebs and others made their way out of Germany,
one by one. During this period, both the KWG and Krehl encouraged
Meyerhof to remain in Heidelberg and continue with his important
research. Initially, this support and his prestige as a Nobel
Prize winner helped to shield Meyerhof and his family from the
excesses of the Nazis. Like so many others, Meyerhof was convinced
that the National Socialists were unlikely to maintain their
grip on power and, because his work at the Physiology Institute
was proceeding so marvelously, he chose to remain in Germany
- dangerously late as would become clear in retrospect.

It was not until 1937 that Meyerhof began
making secret plans to leave the country. Writing in code, his
former assistant David Nachmansohn arranged for a position in
France for his old professor. Having already sent his two older
children abroad, Meyerhof and his wife Hedwig received special
permission in 1938 to pass into Switzerland for medical treatment
of their youngest son. Once across the border, they then made
their way safely on to Paris. To protect the deception, Meyerhof
told none of his colleagues of his departure. Unfortunately,
this also meant he was forced to leave behind all of his scientific
data and personal possessions. Two years later, the German invasion
of France sent the Meyerhofs on another harrowing journey across
the Pyrénées and Spain to Lisbon, where they boarded
a ship bound for Philadelphia in the USA. Meyerhof worked at
the University of Pennsylvania until his death in 1951.

The Influence of the Meyerhof School

Fritz Lipmann

Severo Ochoa

André Lwoff

George Wald

Otto Meyerhof was not only an important
figure in the building of the foundations of modern biochemistry,
he also trained a large number of scientists who went on to
carve out outstanding careers in their own right. In addition
to scientists like Kurt Lohmann, David Nachmansohn, W. Kiessling,
and Paul Ohlmeyer, those working with Meyerhof at the KWImF
included four future Nobel Prize winners: Fritz Lipmann, Severo
Ochoa, André Lwoff and George Wald. These scientists
spread out across the globe during the 1930s, helping to bring
about a wave of discovery in the emerging field of biochemistry.
By their own accounts, each was decisively influenced by Meyerhof's
scientific ideas and his personality and maintained close contact
with Meyerhof until his death in 1951.

Lipmann left Heidelberg for Denmark, finally
settling in the USA at the start of WWII. In the early 1940s,
Lipmann extended our understanding of bioenergetics by formulating the
concept of the ATP metabolic wheel and introducing his famous "wiggle" (~P)
to represent the bonds of high energy phosphate
derivatives. In 1953, he was awarded the Nobel Prize for his
discovery of co-enzyme A and its importance for intermediary
metabolism.

Severo Ochoa spent two different periods
at the KWImF - first in 1930-31 and again in 1936-37, during
which he analyzed enzymatic steps of glycolysis and fermentation.
He later worked with the Coris and, like Lipmann, settled permanently
in the United States. Ochoa's later research dealt principally
with enzymatic processes in biological oxidation and synthesis
and the transfer of energy. In 1959, he was awarded the
Nobel Prize for discovery of the mechanisms involved in the
biological synthesis of ribonucleic acid.

While working with Meyerhof in Heidelberg,
André Lwoff studied haematin - a growth factor for the
flagellates - the specificity of protohaematin, its quantitative
effect on growth, and the part it played in the respiratory
catalyst system. Lwoff settled in Paris in the late 30s, where
he began studying bacteria and viruses. In the 1950s, he joined Jacques Monod and François Jacob in
building the foundation of French molecular biology. Together,
they were awarded the Nobel Prize in 1965 for their discoveries
concerning genetic control of enzyme and virus synthesis.

George Wald first identified vitamin A in
the retina while working with Otto Warburg in 1930. Vitamin
A had just been isolated in the laboratory of Paul
Karrer in Zurich and Richard Kuhn at the KWImF. At Warburg's
suggestion, Wald moved on to the KWImF to take advantage of
the creative insights of Meyerhof and Kuhn. Wald returned to
the United States in 1934. Thirty-three years later, he won
the Nobel for his discoveries concerning physiological and chemical
visual processes in the eye.

The Personality of Meyerhof

Otto Meyerhof was born in 1884
in Hannover, Germany. His father had come from a small
Jewish enclave in the nearby city of Hildesheim -
notable largely because the Hildesheim Meyerhofs had
extensive kinship relations with the families of two
other scientists who knew Meyerhof well and became
fellow pioneers of modern biochemistry - Hans Krebs
and Carl Neuberg.

Otto
MeyerhofPhoto: Courtesy of Walter Meyerhof, son of Otto Meyerhof

As a youth, Meyerhof's relationship
with his mother was particularly close. It was she
who encouraged him to harness his intellectual abilities.
Meyerhof quickly demonstrated a broad range of interests
that included music, art, natural sciences, history
and architecture. He became an accomplished pianist,
wrote poetry and soon developed a passionate interest
in the philosophy of Kant and Fries. A later attraction
to quantum physics was based as much in his fascination
with the epistemological questions raised by Einstein, Heisenberg, Bohr, as it was for
scientific considerations.

Meyerhof demonstrated an early professional tendency toward
multidisciplinarity. Although he studied medicine, his humanistic
interests were reflected in a dissertation on a topic in
psychiatry. And during his career in biological research,
he was largely successful because of his ability to integrate
chemistry, physics and physiology into a single cohesive
approach.

Anti-Semitism had a profound effect on Meyerhof's professional
and personal life, even before Hitler came to power. Nevertheless,
Meyerhof's decision to flee the country in 1938 weighed
heavily on him. Meyerhof may have been Jewish, but Germany
was his homeland. Moreover, as he feared, he was never again
provided with the rich scientific resources that were at
his disposal at the KWImF. The years that followed immediately
were depressing times for Meyerhof. Although he, his wife
and children escaped safely from the holocaust, the family
lost almost all of its possessions, including Meyerhof's
beloved library. And yet, Meyerhof continued to draw strength
from his philosophical approach to life and his professional
career, in which he remained active until his death in 1951.

In retrospect, one is struck by the dignity and generosity
Meyerhof demonstrated towards others throughout his career.
Assistants and competitors alike found that he listened
closely and respectfully to their ideas, whether he agreed
or not. To his assistants and students in Heidelberg, he
was both a mentor and true friend - an unusual practice,
given the elevated stature of senior scientists and the
formality of the time.